Automatic articulation machine states

ABSTRACT

A controller monitors groundspeed in an articulated machine and selectively disables an automatic articulation control function when the groundspeed is at or near zero. If there is an indication that an operator may not be aware that the automatic articulation control function is active by comparing when a on switch was activated compared to a machine power cycle or an operator not being present, the automatic articulation control function may be inactivated until the on switch is toggled. If the articulated machine is in neutral and the groundspeed is at or near zero, the automatic articulation control function may disabled. If the groundspeed is at or near zero but the transmission is not in neutral, the machine may simply be stalled to due working conditions and the automatic articulation control function may be maintained.

TECHNICAL FIELD OF THE DISCLOSURE

The present disclosure generally relates to articulated machines such asmotor graders and, more particularly, relates to a system and method forautomatically controlling articulation of an articulated machine.

BACKGROUND OF THE DISCLOSURE

An articulated machine, such as a motor grader, is a versatile apparatusfor road work, ditch work, site preparation and other surface contouringand finishing tasks. The versatility of a motor grader is provided inlarge part by its multiple course setting and course change options. Inparticular, a motor grader typically includes a steering functionimplemented via steerable ground engaging wheels while also allowingsome degree of course correction or steering via lateral arching orarticulation of the machine frame. In this manner, for example, a motorgrader may be steered and articulated to follow a curve without drivingthe rear wheels across the area inside the curve and disturbing the justgraded area.

As should be recognized from the above, motor graders, and otherarticulated machines, are complex pieces of heavy machinery and areoperatively complex. Controlling a motor grader includes numeroushand-operated controls to steer the front wheels, position the blade,control articulation, control auxiliary devices such as rippers andplows, and various displays for monitoring machine conditions and/orfunctions. Control of a motor grader requires highly skilled and focusedoperators to position the blade while controlling steering.

Automatic articulation control can help relieve an operator of anarticulated machine from the moment-to-moment monitoring of articulationwhile making turns but for reasons including safety, such system may bedisengaged under different conditions, such as when the speed of avehicle exceeds a threshold speed. For example, U.S. Patent ApplicationPublication 2011/0035109 (“Steering System with Automated ArticulationControl”) describes a system wherein machine articulation isautomatically controlled based on machine steering. The system of the'109 publication adjusts machine articulation to follow steering anglesand commands, thereby maintaining tracking between the front and rearwheels of the machine. Automated articulation may be automaticallydisengaged when the ground speed of the machine exceeds a limit.

However, there may be situations where an operators expectations ofautomatic articulation control is different from the actual state, whichcan cause operational difficulties or even a safety hazard.

SUMMARY OF THE DISCLOSURE

In accordance with one aspect of the present disclosure, a method ofmanaging articulation in an articulated machine using an electroniccontroller includes determining, at the electronic controller, that thearticulated machine is operating at a groundspeed below a minimumthreshold speed. Responsive to determining that the articulated machineis operating below the minimum threshold speed, the electroniccontroller may disable an automatic articulation control function whenone of either a first state or a second state is true. The first stateis when a transmission of the articulated machine is in neutral and thesecond state is when a mode selector is set continuously on from priorto a machine key cycle, a machine power cycle, or an ‘operator notpresent’ state.

In another aspect of the disclosure, a system for managing articulationin an articulated machine includes a controller that implements anautomatic articulation control function in the articulated machine. Thecontroller may include a processor, at least one sensor input thatreceives a groundspeed of the articulated machine, and a memory storingdata and computer-executable instructions. When the computer-executableinstructions are executed by the processor is causes the controller todetermine that a mode selector is in an on state, compare thegroundspeed of the articulated machine to a minimum speed, and when thegroundspeed is below the minimum speed, determine that a conditionexists that precludes operation of the automatic articulation controlfunction. The controller may then prevent the automatic articulationcontrol function from changing an articulation angle of the articulatedmachine.

In yet another aspect of the disclosure, a method of operating acontroller that manages articulation angle in an articulated machine mayinclude identifying that a mode selector is in an on position. When agroundspeed of the articulated machine is below a threshold speed, themethod may identify that a predetermined operating condition is true,and may prevent the controller from changing the articulation angle ofthe articulated machine.

Other features and advantages of the disclosed systems and principleswill become apparent from reading the following detailed disclosure inconjunction with the included drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a motor grader constructed in accordance withthe present disclosure;

FIG. 2 is a top view of the motor grader of FIG. 1;

FIG. 3 is a schematic top view of a motor grader during an automaticarticulation mode of operation in accordance with the presentdisclosure;

FIG. 4 is a block diagram of an exemplary steering control system inaccordance with the present disclosure; and

FIG. 5 is a simplified illustration of a cab control for an automaticarticulation control function;

FIG. 6 is a flow chart depicting a process of implementing an automaticarticulation control function;

FIGS. 7-10 are exemplary transfer functions related to full range andnon-linear articulation to steering angle control; and

FIGS. 11-12 are prior art transfer functions related to partial rangesteering control angle.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure provides a system and method that uses anautomatic articulation system for enabling an operator of a motor graderor other articulated machine to optimize use of the articulationcapabilities of the articulated machine. In particular, the system andmethod may employ a controller that prevents automatic articulationcontrol functions from starting or disables automatic articulationcontrol when any of a number of conditions are detected. In addition,some automatic articulation control features may allow limited operationto correct an undesired articulation angle prior to disabling orsuspending operation. As disclosed below, the automatic articulationcontrol functions improve both safety and ease of use as well asproviding additional articulation tracking modes.

FIG. 1 is a schematic side view of an articulated machine 10,specifically, a motor grader in accordance with an embodiment of thepresent disclosure. The articulated machine 10 includes a front frame12, rear frame 14, and a work implement 16, e.g., a blade assembly 18,also referred to as a drawbar-circle-moldboard assembly (DCM). The rearframe 14 includes a power source (not shown), contained within a rearcompartment 20, that is operatively coupled through a transmission (notshown) to rear traction devices or wheels 22 for primary machinepropulsion.

As shown, the rear wheels 22 are operatively supported on tandem axels24 which are pivotally connected to the machine between the rear wheels22 on each side of the articulated machine 10. The power source may be,for example, a diesel engine, a gasoline engine, a natural gas engine,or any other engine known in the art. The power source may also be anelectric motor linked to a fuel cell, capacitive storage device,battery, or another source of power known in the art. The transmissionmay be a mechanical transmission, hydraulic transmission, or any othertransmission type known in the art. The transmission may be operable toproduce multiple output speed ratios (or a continuously variable speedratio) between the power source and driven traction devices.

The front frame 12 typically supports an operator station 26 thatcontains operator controls 106, along with a variety of displays orindicators used to convey information to the operator, for primaryoperation of the articulated machine 10. The front frame 12 may alsoinclude a beam 28 that supports the blade assembly 18 and which isemployed to move the blade 30 to a wide range of positions relative tothe articulated machine 10. The blade assembly 18 includes a drawbar 32pivotally mounted to a first end 34 of the beam 28 via a ball joint (notshown) or the like. The position of the drawbar 32 is typicallycontrolled by hydraulic cylinders: a right lift cylinder 36 and leftlift cylinder 38 (FIG. 2) that control vertical movement, and a centershift cylinder 40 that controls horizontal movement. The right and leftlift cylinders 36, 38 are connected to a coupling 70 that includes liftarms 72 pivotally connected to the beam 28 for rotation about axis C. Abottom portion of the coupling 70 may have an adjustable lengthhorizontal member 74 that is connected to the center shift cylinder 40.

The drawbar 32 may include a large, flat plate, commonly referred to asa yoke plate 42. Beneath the yoke plate 42 is a circular geararrangement and mount, commonly referred to as the circle 44. The circle44 is rotated by, for example, a hydraulic motor referred to as thecircle drive 46. Rotation of the circle 44 by the circle drive 46rotates the attached blade 30 about an axis ‘A’ perpendicular to a planeof the drawbar yoke plate 42. The blade cutting angle is defined as theangle of the work implement 16 relative to a longitudinal axis 48 of thefront frame 12. For example, at a zero degree blade cutting angle, theblade 30 is aligned at a right angle to the longitudinal axis 48 of thefront frame 12 and beam 28 (FIG. 2).

The blade 30 is also mounted to the circle 44 via a pivot assembly 50that allows for tilting of the blade 30 relative to the circle 44. Ablade tip cylinder 52 is used to tilt the blade 30 forward or rearward.In other words, the blade tip cylinder 52 is used to tip or tilt a topedge 54 relative to the bottom cutting edge 56 of the blade 30, which iscommonly referred to as a blade tip. The blade 30 is also mounted to asliding joint associated with the circle 44 that allows the blade 30 tobe slid or shifted from side-to-side relative to the circle 44. Theside-to-side shift is commonly referred to as blade side shift. A sideshift cylinder (not shown) or the like is used to control the blade sideshift.

Motor grader steering is accomplished through a combination of bothfront wheel steering and machine articulation. As shown in FIG. 2,steerable traction devices, such as right and left wheels 58, 60, areassociated with the first end 34 of the beam 28. Wheels 58, 60 may beboth rotatable and tiltable for use during steering and leveling of awork surface 86 (FIG. 1). Front wheels 58, 60 are connected via asteering apparatus 88 that may include a linkage 90 and a hydrauliccylinder (not shown) for rotation at front wheel pivot points 80, FIG.3, and tilt cylinders 92 for front wheel tilt. Front steerable wheels58, 60 and/or rear driven traction devices 22, may include tracks,belts, or other traction devices as an alternative to wheels as is knownin the art. The front wheels 58, 60 may also be driven, as is the casein motor graders provided with all wheel drive. For example, the powersource may be operatively connected to a hydraulic pump (not shown)fluidly coupled to one or more hydraulic motors (not shown) associatedwith the front wheels 58, 60.

Referring to FIGS. 1 and 3, the articulated machine 10 includes anarticulation joint 62 that pivotally connects front frame 12 and rearframe 14. Both a right articulation cylinder 64 and left articulationcylinder 66 (FIG. 3) are connected between the front frame 12 and rearframe 14 on opposing sides of the articulated machine 10. The right andleft articulation cylinders 64, 66 are used to pivot the front frame 12relative to the rear frame 14 about an articulation axis B (FIG. 1). InFIG. 2, the articulated machine 10 is positioned in the neutral or zeroarticulation angle position with the longitudinal axis 48 of the frontframe 12 aligned with a longitudinal axis 68 of the rear frame 14.

FIG. 3 is a schematic top view of a articulated machine 10 with thefront frame 12 rotated at an articulation angle α defined by theintersection of longitudinal axis 48 of front frame 12 and longitudinalaxis 68 of the rear frame 14, the intersection corresponding with theposition of articulation joint 62. In this illustration a positive α isindicative of a left articulation from the perspective of an operatorfacing forward, while a negative α (not shown) would be indicative of aright articulation. A front wheel steering angle θ is defined between alongitudinal axis 76 parallel to the longitudinal axis 48 of front frame12, and a longitudinal axis 78 of the front wheels 58, 60, the angle θhaving an origin at a pivot point 80 of the front wheels 58, 60. This isdemonstrated in connection with right front wheel 58, but equallyapplies to left front wheel 60. As with articulation angle, a positive θis defined as the front wheels 58,60 being to the left of longitudinalaxis 76 and a negative θ defined as the front wheels 58, 60 being to theright of longitudinal axis 76.

In the interest of brevity and minimization of any risk of obscuring theprinciples and concepts in accordance to the present disclosure, unlessother specified, the description of steering angles and articulationangles are assumed to be magnitudes with absolute values. That is, arange of 0 degrees to 20 degrees of articulation refers to 0 degrees to+20 degrees and 0 degrees to −20 degrees. Similarly, a range of steeringangle of 0 degrees to 12 degrees refers to a range including both 0degrees to +12 degrees and 0 degrees to −12 degrees. Another steeringangle range of +12 degrees to 50 degrees includes steering angles of +12degrees to +50 degrees and −12 degrees to −50 degrees. Lastly, steeringangle ranges and articulation angle ranges are assumed to havenon-overlapping values, so that when one range is, for example, asteering angle of 0 degrees to +12 degrees and another range is +12degrees to +50 degrees, one value is either slightly higher or lowerthan exactly 12 degrees.

With reference now to FIG. 4, a block diagram of an exemplary steeringcontrol system 100 in accordance with an embodiment of the disclosure isprovided. The control system 100 generally includes an electroniccontroller 102 configured, for example, via a control algorithm, toreceive a plurality of instructions from various sensors and/or operatorcommands, and to responsively provide instructions to control variousmachine actuators and/or communicate with the machine operator.Controller 102 may include various components for executing softwareinstructions designed to regulate various subsystems of the articulatedmachine 10. For example, the controller 102 may include a processor 103,a memory 105, that may include a random access memory (RAM) and aread-only memory (ROM). The memory 105 may also include a mass storagedevice, data memory, and/or on a removable storage medium such as a CD,DVD, and/or flash memory device, but does not include propagated mediasuch as a carrier wave. The controller 102 may execute machine readableinstructions stored in the memory 105. The controller 102 may alsoinclude input/output hardware 107 coupled to various sensors and outputdevices described below.

The control system 100 may be configured to control machine articulationfor machine articulation based upon operator control of the front wheelsteering. Accordingly, the controller 102 may be configured to receivean indication of the front wheel steering angle θ. In some examples, thearticulated machine 10 includes one or more steering angle sensors 104that may be associated with one or both of the right and left frontwheels 58, 60. In some such examples, the steering angle sensor 104 isconfigured to monitor the wheel steering angle θ by monitoring angles ofrotation of steering linkages and/or pivot points at the front wheels.

The steering angle sensors 104 may be configured to monitor the wheelsteering angle by measuring the extension amount of an actuator (notshown), such as a hydraulic actuator, that controls the steering offront wheels 58, 60. Other sensor configurations are well known in theart. The steering angle sensors 104 may provide data “indicative of” thesteering angle, which should be understood to mean direct measurementsof the quantity or characteristic of interest, as well as indirectmeasurements, for example of a different quantity or characteristichaving known relationships with the quantity or characteristic ofinterest.

The controller 102 may be configured to receive a signal from one ormore operator steering controls 106 that may be employed to provide anindication of steering angle θ. These controls 106 may be, for example,a steering wheel 106 as shown in FIG. 1-2, or any other type of operatorinput device, such as a dial, joystick, keyboard, pedal or other devicesknown in the art. In one embodiment, for example, a steering wheelsensor may be provided that senses the rotation or position of thesteering wheel 106 to provide an indication of steering angle θ. Whetherreceived via the steering angle sensors 104 or operator steeringcontrols 106, a steering signal may be generated that is used in thecontroller to determine a steering angle of the front wheels 58, 60.

One or more articulation sensors 108 may be employed to provide anindication of the articulation angle α at the axis B between the rearframe 14 and front frame 12. In some examples, the articulation sensor108 is a pivot sensor disposed at articulation joint 62 to senserotation at articulation axis B. Additionally or alternatively, thearticulation sensor 108 may be configured to monitor the extension ofright and/or left articulation cylinders 64, 66. Steering angle sensors104 and articulation sensors 108 could be any type of sensor known inthe art, including, for example, potentiometers, extension sensors,proximity sensors, angle sensors and the like.

Other inputs that may be associated with the control system 100 mayinclude instructions provided from a mode selector 110 disposed, forexample, in operator station 26. The mode selector 110 may include aslider 214 for selecting an operating mode and a dial 216 for selectinga steering angle to articulation angle mode, discussed more below. Theoperating mode may be employed to select among various modes ofoperation including, for example, a manual mode, or one or moreautomatic modes. Other input mechanisms and selections may also be used.

Addition inputs may include machine speed sensors 112 and transmissionsensors 114 located, for example, in rear compartment 20. Machine speedsensors 112 may be any sensor configured to monitor machine travelspeed, for example, sensors associated with any of the front wheels,rear wheels, axle shafts, motors, or other components of the drivetrain. A transmission sensor 114 may be associated with the transmissionto provide an indication of a current gear or output ratio.Alternatively, an indication of current gear or output ratio may beprovided by data associated with operator controls for the transmission(not shown).

The control system 100 may also include outputs that affect operation ofthe articulated machine 10. Power steering instructions 118 may beprovided to control steering actuators 120. Articulation actuators 64,66 may be controlled by articulation control instructions 122 that mayresult, depending on operating mode, from either operator input viaarticulation controls 116 or developed automatically at controller 102.A state or mode of operation of the automated articulation function maybe transmitted to an operator via communication instructions 124 anddisplay panel 126.

Referring to FIG. 5, a cab control 125 for the automatic articulationcontrol function may include a mode selector 110, discussed above, and adisplay panel 126. The display panel 126 may include an “On” indicator202 and an ‘Inactive” indicator 204. The Inactive indicator 204 maygenerally indicate that one or more conditions is preventing activationof the automatic articulation control function. In the illustratedembodiment, more than one indicator may be used to represent some of thedifferent operating states separately, such as “Armed” 206,“Center-Only” 208 and “Error Condition” 210. Under some conditions, morethan one display may be active at a time, such as ‘Error Condition’ 210and ‘Inactive’ 204. In some embodiments, a message area 212 may providemore detailed information to an operator or may provide instructions forthe operator on steps to take should the automatic articulation controlfunction be in one of the indicated states. In different embodiments,other indicators and combinations of display technology can used toreceive mode selections and to convey information about the state of theautomatic articulation control function, related messages, and helpinformation. These display technologies may include touch screens, voicerecognition, etc.

INDUSTRIAL APPLICABILITY

FIG. 6 illustrates an exemplary control process 300 for managingautomatic articulation behavior. The control process may be executed bya processor 103 of the controller 102 using computer-executableinstructions stored in the memory 105.

At a block 302, the position of the mode selector 110 may be determinedthrough known mechanisms. If the mode selector is in one of theautomatic mode selection positions execution may continue to block 304.If the speed of the articulated machine 10 is below a threshold speed,for example, less than one or two miles per hour including stopped, the‘yes’ branch may be followed to a block 306.

Generally, at block 306, when the mode selector 110 is set to anautomatic operation setting, a determination is made if the articulatedmachine 10 is in a state where the operator may not be aware of theautomatic articulation mode setting. Without a safety override,automatic articulation may occur without the operator expecting it.Changes in articulation angle alter the steering pattern of the vehicle,so if such changes occur when an operator does not expect it, thearticulated machine 10 may turn differently than anticipated and couldresult in an accident.

So, at block 306, conditions are checked that indicate an operator maynot be aware that the mode selector 110 is set to on. These conditionsmay include a machine key cycle or machine power cycle. That is, thatwhen the engine was last started, the mode selector 110 was set to an“ON” position. Another exemplary condition may be when a seat or cabsensor indicates that no operator is present when the mode selector 110is set to an on position. In these cases, an operator may not be awareof a pre-existing automatic articulation mode selection.

If any of these exemplary conditions, or other similar conditions areidentified, the ‘yes’ branch from block 306 may be followed to block308. At block 308, the automatic articulation control function may bedisabled or inhibited. This does not represent, necessarily, an errorcondition, and may simply require that the operator toggle the modeselector 110 to “OFF” and back to “ON”, as indicated at block 310. Anappropriate indicator may be activated at the display panel 126. Aftertoggling the mode selector 110, execution may return to block 304. In anembodiment, these conditions can disable the automatic articulationcontrol function independently of groundspeed. That is, alternatecontrol processes may evaluate these factors independently fromgroundspeed checking or in parallel with groundspeed checking.

If, at block 304, the groundspeed of the articulated machine 10 is belowthe threshold speed, the ‘yes’ branch may be taken, as before, to block306. At block 306, if the conditions associated with inhibitingoperation of the automatic articulation control function are clear, the‘no’ branch from block 306 may be taken to block 312.

At block 312, a check may be made to determine if the transmission is inneutral, for example using transmission sensor 114. Because thetransmission is in neutral and groundspeed is at or near zero, anassumption may be made that the vehicle is parked or stopped. However,even while stopped an operator or maintenance person may turn the frontwheels 58, 60 to check for tire condition or to access a mechanicalcomponent for inspection or maintenance. Similar to the conditionsabove, should an operator turn the front wheels 58, 60 while the vehicleis not moving, and if there were no check for this condition, thearticulated machine 10 may change its articulation angle causing thefront frame 12, rear frame 14, or both to move. Such unexpected movementcould injure personnel or damage nearby equipment or buildings.Therefore, if the transmission is in neutral, the ‘yes’ branch fromblock 312 may be taken to block 326 and the automatic articulationcontrol function may be disabled or inhibited. Once disabled, theautomatic articulation control function may be re-activated according tothe steps beginning at block 302. An appropriate indicator may beactivated at the display panel 126.

Returning to block 312, if the speed of the articulated machine 10 isbelow the threshold speed and none of the inhibit conditions arepresent, and if the transmission is not in neutral an assumption may bemade that the articulated machine 10 is operating normally and executionmay continue at block 314 or, in an embodiment block 318 (notspecifically depicted). For example, the articulated machine 10 may beoperating on a steep uphill grade or may be scraping a heavy ordifficult work surface 86 that causes the machine 10 to come to amomentary halt or at least to slow below the threshold speed. In thissituation, if the automatic articulation control function wereautomatically disabled it could create an inconvenience at the least andat the most cause a safety hazard should the operator be expectingautomatic articulation when unbeknownst to him or her it had beendisabled. The decision point at block 312 allows automatic articulationcontrol to continue functioning in this situation for both safety andconvenience reasons. Note that this condition is normally only bereached when the automatic articulation control function is alreadyactive and operating.

Returning to block 304, if the groundspeed of the articulated machine 10is greater than the threshold speed the ‘no’ branch may be taken fromblock 304 and execution may continue at block 314. At block 314, anactual articulation angle and a desired articulation angle may becompared. A value of actual articulation angle may be determineddirectly or indirectly from data received via articulation sensors 108.Desired articulation angle may be calculated based on inputs fromsteering controls 106 and/or steering angle sensors 104, that is, byevaluating a current steering angle to determine the desiredarticulation angle. In some embodiments, the current steering angle todesired articulation angle may be a function of a nonlinear transferfunction or some other mapping algorithm, as described in more detailbelow.

Any of several conditions may contribute to an actual articulation anglenot being equal to a desired articulation angle. In one case, anoperator may engage the automatic articulation control function, e.g. atblock 302, when the current steering angle dictates a desiredarticulation angle that is simply not equal to the current articulationangle. For example, the articulated machine may be in alignment withzero articulation angle and the steering wheels oriented in a 35 degreeleft turn. In another example discussed more below, an error conditionthat has caused the automatic articulation control function totemporarily be disabled may clear but the actual and desiredarticulation angles may have diverged during the time when the automaticarticulation control function was disabled. Activation of the automatedarticulation in these cases could cause a sudden and dramatic change inarticulation angle and could cause changes to steering that may bedifficult or impossible for an operator to control. In a worst-casescenario, if articulation were at −20 degrees and steering were at +45degrees, activation of the automatic articulation control function wouldcause the rear frame 14 to rapidly move a full 40 degrees.

In some prior embodiments of automatic articulation control an operatormight be required to manually observe the steering angle of the frontwheels 58, 60 as well as the current articulation angle and attempt toactivate the automatic articulation control function at an exact timewhen the two angles appear to be in alignment. This was found to be bothdifficult and a significant distraction to an operator.

At block 314, when the actual and desired articulation angles are notequal, or within a threshold angle range such as 0.2 degrees to −0.2degrees the ‘no’ branch may be taken to block 320.

At block 320, the automatic articulation control function may be armed,that is, in a standby state so that the electronic controller 102 canmonitor the actual and desired articulation angles and when they arewithin the threshold angle range engage the automatic articulationcontrol function. This relieves the operator of the need to manuallyobserve and time activation of the function but preserves the desirablecharacteristic of avoiding a rapid and significant change inarticulation angle of the articulated machine 10 when engaging theautomatic articulation control function.

When at block 314 the actual and desired articulation angles are at zeroor are within the threshold angle range, the ‘yes’ branch may be takento block 316. At block 316, the controller 102 may screen for any ofseveral error conditions including but not limited to a groundspeed ofthe articulated machine 10 being over a limit, an invalid signal orinput signal such as no groundspeed signal being available at thecontroller 102, or other errors such as steering sensor errors. In anembodiment, the maximum limit for groundspeed or threshold groundspeedmay be about 20 mph, but may vary for different kinds of articulatedmachines 10 or even for different operation conditions. When no errorconditions are found, execution may follow the ‘no’ branch to block 318.

At block 318, the automatic articulation control function may beactivated and control articulation of the articulated machine 10according to whatever control strategy is active. More details ondifferent control strategies are discussed below with respect to FIGS. 7through 10.

In an exemplary embodiment, the articulated machine 10 may be operatedat an articulation angle α with a magnitude greater than zero betweenthe front frame 12 and the rear frame 14 responsive to instructions fromthe electronic controller 102. For example, from a fully alignedposition when the front wheels 58, 60 turn to the left (+θ) theelectronic controller 102 may cause the articulated machine 10 toarticulate to the left, designated as a positive articulation angle or+α. Similarly, from a fully aligned position when the front wheels 58,60 turn to the right (−θ) the electronic controller 102 may cause thearticulated machine 10 to articulate to the right designated as anegative articulation angle or a −α. Whether articulated to the left orto the right, a magnitude of the angle α is non-zero whenever the frontframe 12 and rear frame 14 are not aligned.

Returning to block 316, when an error condition is present the ‘yes’branch from block 316 may be taken to block 322. At block 322, adetermination is made as to whether the articulated machine 10 is in anarticulated state with a non-zero articulation angle, that is, with amagnitude outside a threshold angle range discussed above.

If at block 322, the articulated machine 10 is not articulated executionmay take the ‘no’ branch to block 326 and the automatic articulationcontrol function may be disabled. An appropriate indicator may beactivated at the display panel 126.

If, at block 322, the articulated machine 10 has some nonzero angle ofarticulation, were the automatic articulation control function simplydisabled, the articulated machine 10 may be fixed at some angle ofarticulation that is counterproductive to future steering anglesettings. For example, if an articulated machine 10 is in a left-handturn with a steering angle of +20 degrees and a correspondingarticulation angle of +20 degrees at which time the ground speedincreases above a groundspeed limit, simply disabling the automaticarticulation control function would cause the articulation angle toremain at a +20 degree angle of articulation even though a steeringangle may change to the right through zero or beyond. This would createan awkward situation where the machine is articulated to the left andthe steering is articulated to the right, causing the articulatedmachine 10 to “crab” along the work surface.

To avoid this situation, execution may continue at block 324. At block324, the automatic articulation control function may be configured tooperate in a return-to-zero mode so that it responds only to steeringcommands that would cause the articulation angle to return to zero. Thatis, any detected steering angle that would increase the desiredarticulation angle is ignored and any detected steering angle thatcauses the desired articulation angle to decrease is processed. When thearticulation angle decreases to zero, or is within the minimum thresholdangle range, execution continues at block 326 and the automaticarticulation control function is disabled.

When, at block 316, the error condition has cleared and the actual anddesired articulation angles are approximately equal at block 314 theautomatic articulation control function may be reactivated and normaloperation continued at block 318.

The exemplary control process 300 of FIG. 6 is but one representation ofsteps that may be followed to implement the controls and featuresdisclosed. A person of ordinary skill in the art would recognize thatother implementations could be developed that implement the safety andcontrol functions discussed above. For example, various inhibit anderror conditions could drive interrupts so that automatic articulationcontrol could be performed via a state change paradigm.

FIGS. 7-10 illustrate exemplary transfer functions related to full rangeand non-linear steering angle to articulation angle control. Thesefigures illustrate an exemplary embodiment where steering angle canrange from about −50 degrees to +50 degrees and articulation angle canrange from about −20 degrees to +20 degrees. Other articulation machinesmay have different steering and articulation angle ranges. Theprinciples disclosed here apply to those different ranges as well.

The articulation angle transfer functions described below allow anoperator a rich selection of operating modes for automatic articulationcontrol. In various embodiments, the dial 216 portion of the modeselector 110 may be modified to allow individual selection of theseexamples or other similar transfer functions for use in variousoperating environments.

FIG. 7 illustrates a non-linear transfer function 400 of steering angleon the x-axis to articulation angle on the y-axis. The transfer function400 shows a first range 402 with a first slope of about 1 or steeringangle to articulation angle ratio of approximately 1:1 from about −10degrees to about +10 degrees. The transfer function 400 shows a secondrange 406 below about −10 degrees and above 404 about +10 degrees thathas a second slope of about ¼ or about 1 degree of articulation angle to4 degrees of steering angle.

In an embodiment, rather than using a fixed steering angle degree totransition from a first range 402 to a second range 404, 406, thecontroller 102 may use a threshold percentage of steering angle, such asa range of about 45% to 55% of maximum steering angle. The first andsecond ranges 402, 404-406 constituting sub-ranges of the full steeringangle range. Each sub-range has steering angle values that are unique,that is not in common with other sub-ranges.

In contrast to the prior art transfer functions 500 of FIG. 11 or 510 ofFIG. 12, that have a 1:1 correspondence of steering angle toarticulation angle and then cap either articulation or steering, thetransfer function 400 provides at least some change in articulation overthe full range of steering angles. The approximately 1:1 ratio in thefirst range of FIG. 4 may allow the rear wheels to track the frontwheels of the articulated machine 10, for example when grading orscraping around a curve, such as a cul-de-sac. The second range 404, 406above and below about 10 degrees of steering angle allows continuousincreases in articulation angle over the full remaining steering angle,allowing the operator to significantly improve turning radius, whendesired.

FIG. 8 illustrates an alternate embodiment of FIG. 7, showing a transferfunction 408 with a first range 410 having a first ratio and a secondrange 412, 414 having a second, lower ratio of steering angle toarticulation angle. The embodiment of FIG. 8 shows ‘porch’ regions 416,418 that illustrate an embodiment where the final few degrees ofsteering angle do not change the articulation angle. The principal ofFIG. 7 is maintained in that the separate transfer function slopes ofthe first and second ranges allow a front-to-back wheel tracking region(range 410) and a less than 1:1 region (range 412, 414).

FIG. 9 illustrates an alternate embodiment from FIGS. 7 and 8 andillustrates a transfer function 420 with one region 422 having aconstant slope with a rate of more than one degree of steering angle toone degree of articulation angle. The transfer function 420 offersconsistent steering to articulation changes over the full range ofsteering angles and offers an operator a predicable rate of change ofarticulation, but does not necessarily provide front wheel to back wheeltracking.

FIG. 10 is an alternate embodiment of the transfer function 420 of FIG.9 and illustrates a transfer function 430 with a constant ratio region432 that is less than 1:1 steering angle to articulation angle but withporches 434 and 436 so that articulation does not necessarily track tothe full extent of the steering range.

The exemplary embodiments illustrated in FIGS. 7-10 may be modified withadditional regions having various linear or non-linear slopes. The aboveillustrations are not limiting with respect to additional variations oftransfer curve implementations.

The exemplary embodiments illustrated in FIGS. 7-10 may also haveapplicability to special cases when operating in reverse. For example,an operator-initiated signal may indicate a desired steering path, orsteering path change. When traveling in the forward direction this maymost naturally take place by sending a signal that controls front wheelsteering angle. However, in some cases, it may be advantageous to firstadjust articulation angle and have the steerable wheels track theadjustment to articulation angle. This may be particularly true whenoperating in reverse.

Another mode of automatic articulation control may be supported thatallows such directional control to be accomplished when operating inreverse through adjustments to the articulation angle operator control,generally via a joystick (not depicted), which then drives changes tothe steering angle. The changes to the steering angle based onarticulation angle may use the same variations of transfer functionsdiscussed above that incorporate a more than 1:1 ratio of steering angleto articulation angle to map at least a portion of the articulationangle range to steering angle range.

FIGS. 11-12 depict prior art transfer functions related to partial rangesteering control angle. As discussed above, FIG. 11 shows a prior arttransfer function 500 with a constant 1:1 region 502 and zero sloperegions 504 and 506. That is, for any steering angle greater than +20degrees or less than −20 degrees, the articulation angle is fixed at acorresponding +20 degrees or minus 20 degrees.

FIG. 12 illustrates a transfer function 510 with a constant 1:1 region512 and constrained steering regions 514 and 516 where the steering islimited to +20 degrees and −20 degrees respectively when the maximumarticulation angles of +20 and −20 degrees are reached.

The present disclosure relates generally to a method of improvingsteering control for an articulated machine having front wheel steering.In general, the disclosed systems receive steering commands from theoperator, and, based upon the steering command or signals indicative offront wheel steering angle, automatically command articulation accordingto a predetermined formula. Automatic control of articulation angle canreduce operator distractions during operation, improve turning radius,cause the rear wheels to track in the path of the front wheels, etc.

The automatic articulation mode is instantiated and executed via thecomputerized execution of instructions stored on a physically-embodiedcomputer-readable medium or memory, e.g., a disc drive, flash drive,optical memory, ROM, etc. The controller 102 may be physically embodiedin one or more controllers and may be separate from or part of one ormore existing controllers such as one or more engine controllers and/ortransmission controllers.

It will be appreciated that the present disclosure provides a system andmethod for facilitating an automatic articulation mode with selectablemodes and enhanced safety and performance features. While only certainembodiments have been set forth, alternatives and modifications will beapparent from the above description to those skilled in the art. Theseand other alternatives are considered equivalents and within the spiritand scope of this disclosure and the appended claims.

What is claimed is:
 1. A method of managing articulation in anarticulated machine using an electronic controller, the methodcomprising: determining, at the electronic controller, that thearticulated machine is operating at a groundspeed below a minimumthreshold speed; and responsive to determining that the articulatedmachine is operating below the minimum threshold speed, disabling, atthe electronic controller, an automatic articulation control functionwhen one of either a first state or a second state is true, the firststate being a transmission of the articulated machine being in neutraland the second state being a mode selector set continuously on fromprior to a machine key cycle, a machine power cycle, or an ‘operator notpresent’ state.
 2. The method of claim 1, further comprising: when theautomatic articulation control function is disabled as a result of thegroundspeed being below the minimum threshold speed and the second statebeing true, determining that a mode selector has been cycled off and on;determining that the groundspeed is above the minimum threshold speed;and enabling the automatic articulation control function to change anarticulation angle of the articulated machine.
 3. The method of claim 1,further comprising: responsive to determining that the articulatedmachine is operating below the minimum threshold speed, maintainingoperation of the automatic articulation control function when neitherthe first state nor the second state are true.
 4. The method of claim 3,wherein the minimum threshold speed is about 0.9 meters per second. 5.The method of claim 1, further comprising controlling articulation ofthe articulated machine based on a steering angle of front wheels of thearticulated machine.
 6. The method of claim 1, further comprising: whenthe automatic articulation control function is disabled as a result ofthe groundspeed being below the minimum threshold speed and one of thefirst or second state being true, providing a notification at anoperator station that the automatic articulation control function isdisabled.
 7. A system for managing articulation in an articulatedmachine, the system comprising: a controller that implements anautomatic articulation control function in the articulated machine, thecontroller comprising: a processor; at least one sensor input thatreceives a groundspeed of the articulated machine; and a memory storingdata and computer-executable instructions that when executed by theprocessor cause the controller to: determine that a mode selector is inan on state; compare the groundspeed of the articulated machine to aminimum speed; when the groundspeed is below the minimum speed,determine that a condition exists that precludes operation of theautomatic articulation control function; and prevent the automaticarticulation control function from changing an articulation angle of thearticulated machine.
 8. The controller of claim 7, wherein the memorystores further computer-executable instructions that when executed causethe processor to: determine that the groundspeed is below the minimumspeed and that no condition is true; and when the groundspeed is belowthe minimum speed and no condition is true, enable the automaticarticulation control function to change the articulation angle of thearticulated machine responsive to changes in a steering angle of frontwheels of the articulation machine.
 9. The controller of claim 7,wherein the condition is the transmission being in neutral.
 10. Thecontroller of claim 7, wherein the condition is the mode selector beingcontinuously on since completion of a machine key cycle.
 11. Thecontroller of claim 7, wherein the condition is the mode selector beingcontinuously on since completion of a power cycle of the articulatedmachine.
 12. The controller of claim 7, wherein the condition is themode selector being continuously on since detecting an ‘operator notpresent’ state.
 13. The controller of claim 7, wherein the memory storesfurther computer-executable instructions that when executed cause theprocessor to: determine that the groundspeed is above the minimum speedand enable the automatic articulation control function to change thearticulation angle of the articulated machine responsive to changes in asteering angle of the front wheels.
 14. The controller of claim 7,further comprising an output that drives an indicator at an operatorstation, the indicator configured to provide a notification that theautomatic articulation control function is disabled when the indicatoris activated by the output.
 15. A method of operating a controller thatmanages articulation angle in an articulated machine, the methodcomprising: identifying that a mode selector is in an on position; whena groundspeed of the articulated machine is below a threshold speed,identifying a predetermined operating condition is true; and preventingthe controller from changing the articulation angle of the articulatedmachine.
 16. The method of claim 15, wherein the predetermined operatingcondition is the transmission being in neutral.
 17. The method of claim15, wherein the predetermined operating condition is the mode selectorbeing continuously on since completion of a machine key cycle.
 18. Themethod of claim 15, wherein the predetermined operating condition is themode selector being continuously on since completion of a machine powercycle of the articulated machine.
 19. The method of claim 15, whereinthe predetermined operating condition is the mode selector beingcontinuously on since detecting an ‘operator not present’ state.